Frequency synthesizers are commonly used in integrated communication systems to provide a carrier frequency. The frequency synthesizers are typically implemented as Voltage Controlled Oscillators (VCOs) using a Phase-Lock Loop (PLL) circuit to stabilize the frequency source and minimize phase noise. An output buffer is often used to amplify the output of the frequency synthesizer and to isolate the frequency synthesizer from load conditions. In portable systems such as cellular telephones, the VCO and the output buffer can be switched on and off to conserve power.